The present invention relates, in general, to image scanning, and in particular, to a microscopic scanner for generating an electronic version of a scanned optical image.
It is often desired to scan an image of a target and then convert that image into an electrical signal for subsequent processing and viewing. Airborne scanners are well-known in which a slit is placed in front of a charge-coupled device (xe2x80x9cCCDxe2x80x9d) array in a camera and the moving aircraft then sweeps (scans) the slit past the target to be scanned as the aircraft flies over the ground. Such scanners have the disadvantage that the airborne scanner platform must move with respect to the target in order to accomplish the scanning.
Other image scanning devices, such as flatbed scanners or drum scanners, are known in which the target is moved past a scanning head so that the image can pass through optics and into a camera and/or onto a CCD array. Such a scanner is disclosed for example in U.S. Pat. Nos. 5,751,420; 5,706,083; and 5,592,291.
In all such prior art devices, the target moves relative to the scanner for each scanned image line, the CCD array remains fixed (non-moving) with respect to the front objective lens of the scanner.
It is also desirable to be able to obtain a spectral representation or imaging spectrograph of the frequency components of an image so that the spectral representation may be further processed to reveal information hidden in the frequency components of the image. For example, in the paper entitled xe2x80x9cAirborne Hyperspectral Image Acquisition with Digital CCD Video Cameraxe2x80x9d, Chengye Mao, Mike Seal, and Gerald Heitschmidt describe an airborne scanning system in which a linear variable filter (xe2x80x9cLVFxe2x80x9d) is placed at the focal plane of a front objective lens, and, as an aircraft transports the scanner over the ground-based target, the linear variable filter separates frequency components of the image that passes by the front objective lens onto a CCD array within a camera. Unlike the present invention, the linear variable filter and CCD array are fixed with respect to the front objective lens, and the scanner must reside on a mobile platform and move past the target in order to accomplish the scanning of the image.
Furthermore, it is desirable to combine the features of a spectrographic instrument or hyperspectral scanner such as described above in a scanning microscope, so that spectral analysis of surface and potentially subsurface features of a sample may be carried out on a microscopic scale. Microscopic hyperspectral scanning of prepared specimens, for example body tissue and fluids and other targets, has great utility in the field of medicine and in the analysis of the physical and mechanical properties of materials. It can also be used to detect the chemical properties of microscopic samples.
An example of a spectral microscopic photometer is disclosed for example in U.S. Pat. No. 5,112,125, in which light from an illuminated sample is collected and measured by means of a series of lenses, diaphragms and photodetectors. Similarly, U.S. Pat. No. 4,631,581 discloses an apparatus for microphotometering of microscopic specimens, which uses both mechanical and electronic scanning techniques to generate a three dimensional image of a target specimen.
As noted previously, however, a disadvantage of each of these devices is that in order to scan the entire surface of the specimen, it is necessary to move the sample relative to the scanning instrument for each scanned image line. For example, in U.S. Pat. No. 5,112,125 a scanning stage which supports the specimen is adjustable along through orthogonal axes, so that it can also be used to carry out time-resolved spectral measurements. Similarly in U.S. Pat. No. 4,631,581, a drive unit is provided to move the sample in order to scan elongated samples.
Scanning becomes extremely difficult to control when a translation of a sub-micrometer level is required for scanning an image line of the specimen under a microscope with high magnification. That is, due to the high magnification of the microscope, all movements of the specimen are enlarged correspondingly and their apparent velocity is multiplied, making positioning of the specimen difficult to control. Also, due to continuous movement of the specimen, any contemporaneous viewing of the specimen through the microscopic eye piece become problematic as well.
It is therefore an object of the present invention to provide an improved image scanner that has a unique feature: instead of directly scanning over the target, it scans a target at its image""s focal plane. Such a scanner is able to perform a uniformed scanning regardless of the target size. For example, the scanning distance will be the same when scanning targets as large as the Earth disk from a geo-stationary satellite or as small as a tiny germ under a microscope.
The present invention is a focal plane scanner having a front objective lens, a spatial window for selectively passing a portion of the image therethrough, and image sampling array means, such as a charge coupled device (xe2x80x9cCCDxe2x80x9d) array, for receiving the passed portion of the image. In particular in the microscopic hyperspectral scanner according to the invention, the front objective lens is a microscopic objective lens.
An essential feature common to all embodiments of the invention is that the spatial window and CCD array are mounted for simultaneous relative reciprocating movement with respect to the front objective lens, with the spatial window being mounted within the focal plane of the front objective lens.
In a first embodiment of the present invention, the spatial window is a slit and the CCD array is one-dimensional. As the slit moves within the focal plane of the front objective lens, successive rows of the image in the focal plane of the front objective lens are passed to the CCD array by an image relay lens interposed between the slit and the CCD array.
In a second embodiment of the present invention, the spatial window is a slit, the CCD array is two-dimensional, and a prism-grating-prism (xe2x80x9cPGPxe2x80x9d) optical spectrometer is interposed between the slit and the CCD array so as to cause the scanned row to be split into a plurality of spectral separations onto the CCD array, with spectral components for each point in the scanned row being separated onto the respective CCD columns for that point.
In a third embodiment of the present invention, the CCD array is two-dimensional and the spatial window is a rectangular linear variable filter (xe2x80x9cLVFxe2x80x9d) window, so as to cause the scanned rows impinging on the LVF to be bandpass filtered into spectral components onto the CCD array through an image relay lens interposed between the LVF and the CCD array.
In a fourth embodiment of the invention, a microscopic objective lens is provided to generate a magnified image of a target specimen which is projected onto the slit, so that rows which make up the image are projected sequentially onto the CCD array as the spatial window and the CCD array are moved in tandem relative to the microscopic objective lens in order to scan an enlarged image of the entire specimen.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.